Screenshots of your set up of the Corona Vol Grid object would be needed. Also would be some information on where the OpenVDB file is from (I presume you mean VDB when you said "vdf file"). Of course rather than do all that you can send us the scene file, which can be done via private uploader if the OpenVDB file is not one that can be redistributed to the public (depends on the license you downloaded it with). And as always, Corona and C4D version and OS are always necessary pieces of info too please :)